JMHO -
Take a minute to introduce myself, explain the crew's background vs. regs, and give enough detail to show how familiar I am with the route, A/C, weather, etc. Also, the pax might actually just be nervous about flying in general and the "youthfulness" is a trigger point, so explain the A/C a bit. This happened to me a couple times at ASA when I was 22.
If that doesn't work, too bad. They can wait for the next one.